The Fallacies Project

In the last 15 years, we have been working on a new account of “fallacies of argumentation”. These fallacies have been described in different ways:

As “traps for unwary reasoners” in the shape of arguments that might seem convincing, but are actually poor arguments, or in terms of a catalogue of argument forms (or “schemes”) that goes back to Aristotle and has been added to over the centuries.

This catalogue includes arguments such as the “argument from ignorance”:

“Ghosts exist because nobody has proven that they don’t”. Though this example does seem weak, others that look very similar don’t:

“This drug is safe, because no side-effects have been found in clinical trials”.

So, it has been hard to find a real explanation of why arguments like the ghosts example are weak that also accounts for why the drug-safety example seems ok. Our account uses probability theory as a standard or yardstick for measuring the quality of arguments, and we can show how that explains why the two arguments differ in strength. This account, we think, provides useful framework for measuring argument quality in many other contexts as well.


Some articles on this topic:

Oaksford, M., & Hahn, U. (2004) A Bayesian approach to the argument from ignorance. Canadian Journal of Experimental Psychology, 58, 121-131.

Hahn, U. & Oaksford, M. (2007) The Rationality of Informal Argumentation: A Bayesian Approach to Reasoning Fallacies. Psychological Review, 114, 704-732.

Hahn, U. & Oaksford, M. (2007) The burden of proof and its role in argumentation. Argumentation, 21, 39-61.

Hahn, Ulrike (2011) The problem of circularity in evidence, argument, and explanationPerspectives on Psychological Science 6 (2), pp. 172-182. ISSN 1745-6916.

Corner, A. and Hahn, U. and Oaksford, M. (2011) The psychological mechanism of the slippery slope argument. Journal of Memory and Language 64 (2), pp. 133-152. ISSN 0749-596X.